Multiphase flow herein above and below is defined as flow of fluids and/or solid particles together as a mixture, but without being completely dissolved in each other. Multiphase flow often occurs as, but not limiting to two-phase flow and three-phase flow. In two-phase flow, either fluids alone or one fluid along with solid particles flow in a flow system, whereas in the three-phase flow, fluids i.e. a gas and a liquid together with solid particles flow in the flow system. Such multiphase flow generally happens in processes such as but not limiting to oil and gas production, where oil and gases that are produced are conveyed in long pipes and channels for subjecting them to further processes, in waste water treatment or sewage treatment plants, slurry and mineral ore transport industries, sludge transport in refining industry, and biological continuous flow cultivation systems.
It is often observed that in the multiphase flow, stratified flow of particles takes place. The stratified flow herein above and below is defined as a flow in which high density particles in the flow mixture may flow at the bottom of the flow channel, and low density particle in the flow mixture may flow above the high density particles. In such stratified flow, the high density particle in the flow mixture may form a secondary phase, whereas the low density particle may form a primary phase. Thus, in the multiphase flow, the secondary phase distribution can become segregated and lead to subsequent settling along the axis of flow. In addition, stratified flow results in poor mass transfer characteristics in the flow systems. Further, the settling down of flow particles in the bottom surface of the flow channel results in following requirements and associated problems such as frequent operations to de-settle the sludge formed in the flow channels, which increases cost of operation in one or more processes stated above. In addition, settling of high density particles in a biological continuous flow cultivation system, such as algae cultivation, results in poor efficiency of cultivation process. In these biological continuous flow cultivation systems, vertical mixing is important for better nutrient homogenization of photosynthetic organisms such as but not limiting to algae. But due to minimal or lack of vertical mixing in the raceway pond, the flow becomes completely stratified, which leads to poor mass transfer of high density particles i.e. algae (or other photosynthetic organisms) and nutrients during the flow.
To overcome the one or more problems stated above, settling of the high density flow particles at the bottom surface of the flow channel should be avoided. In conventional practice, one or more mechanical mixers such as but not limiting to a paddlewheel, is adapted to rotate in a predetermined direction. The movement of the paddlewheel may be along an axis including but not limiting to a horizontal axis, or in a semi-horizontal axis. Similarly a stirrer which is adapted to rotate in a predetermined direction, or along an axis including but not limiting to a vertical axis and a semi-vertical axis, may be employed. Further, a baffle, fixed or moving in a predetermined manner including but not limited to a periodic motion and a rotational motion, have been employed. Typically, all of such mechanical mixers are either partially or fully submerged in a flow channel, and are adapted to move or rotate in respective aforesaid manners for mixing purposes. However, these conventional mechanical mixers require high energy for mixing the flow particles in the flow channel, which increases the cost of the process. Further, the use of mechanical mixers creates mixing only in the local zones around the mixer. Hence, for large-scale processes it is imperative that a large number of such mechanical mixers should be installed. However, in the large scale process it is imperative that power consumption for mixing should be minimum, and yet optimal results should be achieved. However, the use of multiple mixers consumes more energy, and makes the process economically insignificant. In addition to the high energy consumption, utilization of mechanical mixers may lead to problems including but not limiting to, inefficient mixing based on vortices formed behind the mixing blades and settling of solid mass at areas not within the reach of the mixers that have limited dimensions (such as diameters etc.), cavitation and raising of liners in lined bodies of liquid etc.
Further, in fluid mediums such as but not limiting to containers, ponds, wells, reservoirs and vessels it is known to use a means to disturb the fluid to facilitate mixing of the particles present in such fluid mediums. For example, means to disturb the fluid can be such as but not limiting to valves and nozzle arrangement, which can generate disturbance in the fluid medium by further providing fluid inside the fluid mediums. Such an arrangement facilitates mixing of the particles in the fluid medium. However, these conventional means to disturb the fluid require high energy for mixing the particles in the fluid medium, since the fluid has to be impinged at higher velocities, and the particles in the fluid medium would induce resistance since they are settled. This increases the cost of the process and accurate placement of disturbance means to have homogeneous or improved mixing is also a challenge. Further, the resultant mixing may only be achieved at localized regions and may not be entirely satisfactory for continuous flow systems.
As an example, consider a flow cultivation system where biological organisms such as but not limiting to photosynthetic organisms are cultivated in a biological continuous flow cultivation systems such as but not limiting to raceway ponds. In the biological continuous flow cultivation systems, there is a requirement for always keeping the solid particles in the suspended state i.e. solid particles should not be settled at bottom of the raceway ponds. Thus, the flow particles in the raceway ponds are mixed by a mechanical mixer installed in the raceway ponds. In general, mechanical mixer is partially submerged or else fully submerged in pond water at a fixed location, and is adapted to rotate at a fixed speed for mixing purposes. The mixing created by the mechanical mixer is thus localized, i.e., effective only for a small distance in the vicinity of the mechanical mixer. In the rest of the pond, although the flow is turbulent, the vertical mixing is not sufficient for optimal growth of photosynthetic organism. For achieving a uniform and efficient mixing through-out in the raceway pond, a plurality of mechanical mixers are required to be installed at multiple locations to generate turbulence, which in turn proves to be cost-ineffective. However, for a large-scale cultivation for fuel applications, it is imperative that the energy consumption in mixing is kept at minimum and yet optimal growth of algae is achieved. In addition to the high energy consumption, utilization of multiple mechanical mixers may lead to problems including but not limited to inefficient mixing based on vortices formed behind a paddlewheel and settling of solid particles at areas not within the reach of the mechanical mixers that have a limited diameter, cavitation and raising of liners in lined bodies of liquid etc. As explained above the mechanical mixer consumes high energy which in turn increases cost of cultivation of photosynthetic organism.
Limitations of existing conventional mechanical mixers are explained with the help of cultivation of photosynthetic organism (one of the field of applications of the mechanical mixers) as an example. However, such example should not be construed as only application. Thus, person skilled in the art can envisage various other applications where such limitation exists.
In light of foregoing discussion, there exists a need to develop an improved apparatus for mixing multiphase flowing particles in a conduit to overcome one or more limitations as stated above.